This invention is directed to a variable image magnification line scanning-type facsimile in which optical data from a different size original are converted into video signals by a line sensor which are then delivered to a transmitting circuit, and wherein the image size of the original is changed without varying the number of scanning lines which affects the resolution or image quality.
In such an apparatus, a fixed focus lens is generally employed, and the lens or a line sensor is moved to change the distance between an object and its image, to thereby carry out a magnification variation. Alternatively, the focal length of an image forming lens is changed to carry out a magnification variation without changing the distance between an object and its image. In one example of a construction for changing the focal length, a plurality of fixed focus lenses are provided on a disk. That is, a turret type construction is employed in which fixed focus lenses are switched according to the image sizes. In another example, the focal length is varied with a single zoom lens.
In a system wherein the magnification variation is carried out with a fixed focus lens, and wherein the distance between an object is fixed, the line sensor must be moved substantially. Therefore, this method suffers from a problem that in order to make constant the quantity of light received by the line sensor the aperture diameter must be increased or decreased in association with the movement of the line sensor.
In the turret type construction, the disk holding the plurality of fixed focus lenses is turned to switch the lenses to thereby change the focal length. Because of the characteristics of the line sensor, by controlling the quantity of light of the image to a fixed suitable value, the operation range of output of the line sensor can be increased, and accordingly a high contrast video signal can be obtained. Therefore, the numerical aperture of each lens is fixed to a constant value so that the output energy of the line sensor is made constant. However, in the case where the distance between an object and its image is made constant for each of the lenses, it is difficult to obtain a predetermined magnification.
In a facsimile apparatus 100 using the zoom system, as shown in FIG. 4, a single zoom lens 102 is used to continuously change the focal length without changing the distance between the object, or document, 104 and the image formed at the line sensor 106, to thereby change the image size, and therefore a predetermined magnification can be readily obtained. Similarly as in the case of a fixed focus lens, it is necessary to increase or decrease the aperture diameter, in order to make the output energy of the line sensor 106 constant.